[XEN PATCH v3] xen: rework `checkpolicy` detection when using "randconfig"

[Anthony PERARD <anthony.perard@xxxxxxxxxx>]

This will help prevent the CI loop from having build failures when
`checkpolicy` isn't available when doing "randconfig" jobs.

To prevent "randconfig" from selecting XSM_FLASK_POLICY when
`checkpolicy` isn't available, we will actually override the config
output with the use of KCONFIG_ALLCONFIG.

Doing this way still allow a user/developer to set XSM_FLASK_POLICY
even when "checkpolicy" isn't available. It also prevent the build
system from reset the config when "checkpolicy" isn't available
anymore. And XSM_FLASK_POLICY is still selected automatically when
`checkpolicy` is available.
But this also work well for "randconfig", as it will not select
XSM_FLASK_POLICY when "checkpolicy" is missing.

This patch allows to easily add more override which depends on the
environment.

Also, move the check out of Config.mk and into xen/ build system.
Nothing in tools/ is using that information as it's done by
./configure.

Signed-off-by: Anthony PERARD <anthony.perard@xxxxxxxxxx>
---
v3:
- use KCONFIG_ALLCONFIG
- don't override XSM_FLASK_POLICY value unless we do randconfig.
- no more changes to the current behavior of kconfig, only to
  randconfig.

v2 was "[XEN PATCH v2] xen: allow XSM_FLASK_POLICY only if checkpolicy binary 
is available"
---
 Config.mk          |  6 ------
 xen/Makefile       | 18 ++++++++++++++++--
 xen/common/Kconfig |  2 +-
 3 files changed, 17 insertions(+), 9 deletions(-)

diff --git a/Config.mk b/Config.mk
index d0712724f8e4..144411133f38 100644
--- a/Config.mk
+++ b/Config.mk
@@ -137,12 +137,6 @@ export XEN_HAS_BUILD_ID=y
 build_id_linker := --build-id=sha1
 endif
 
-ifndef XEN_HAS_CHECKPOLICY
-    CHECKPOLICY ?= checkpolicy
-    XEN_HAS_CHECKPOLICY := $(shell $(CHECKPOLICY) -h 2>&1 | grep -q xen && 
echo y || echo n)
-    export XEN_HAS_CHECKPOLICY
-endif
-
 define buildmakevars2shellvars
     export PREFIX="$(prefix)";                                            \
     export XEN_SCRIPT_DIR="$(XEN_SCRIPT_DIR)";                            \
diff --git a/xen/Makefile b/xen/Makefile
index f47423dacd9a..89804aefe385 100644
--- a/xen/Makefile
+++ b/xen/Makefile
@@ -17,6 +17,8 @@ export XEN_BUILD_HOST ?= $(shell hostname)
 PYTHON_INTERPRETER     := $(word 1,$(shell which python3 python python2 
2>/dev/null) python)
 export PYTHON          ?= $(PYTHON_INTERPRETER)
 
+export CHECKPOLICY     ?= checkpolicy
+
 export BASEDIR := $(CURDIR)
 export XEN_ROOT := $(BASEDIR)/..
 
@@ -178,6 +180,8 @@ CFLAGS += $(CLANG_FLAGS)
 export CLANG_FLAGS
 endif
 
+export HAS_CHECKPOLICY := $(call success,$(CHECKPOLICY) -h 2>&1 | grep -q xen)
+
 export root-make-done := y
 endif # root-make-done
 
@@ -189,14 +193,24 @@ ifeq ($(config-build),y)
 # *config targets only - make sure prerequisites are updated, and descend
 # in tools/kconfig to make the *config target
 
+# Create a file for KCONFIG_ALLCONFIG which depends on the environment.
+# This will be use by kconfig targets 
allyesconfig/allmodconfig/allnoconfig/randconfig
+filechk_kconfig_allconfig = \
+    $(if $(findstring n,$(HAS_CHECKPOLICY)),echo 'CONFIG_XSM_FLASK_POLICY=n';) 
\
+    $(if $(KCONFIG_ALLCONFIG), cat $(KCONFIG_ALLCONFIG), :)
+
+
+.allconfig.tmp: FORCE
+       set -e; { $(call filechk_kconfig_allconfig); } > $@
+
 config: FORCE
        $(MAKE) $(kconfig) $@
 
 # Config.mk tries to include .config file, don't try to remake it
 %/.config: ;
 
-%config: FORCE
-       $(MAKE) $(kconfig) $@
+%config: .allconfig.tmp FORCE
+       $(MAKE) $(kconfig) KCONFIG_ALLCONFIG=$< $@
 
 else # !config-build
 
diff --git a/xen/common/Kconfig b/xen/common/Kconfig
index 0ddd18e11af3..73d8afb7bcbd 100644
--- a/xen/common/Kconfig
+++ b/xen/common/Kconfig
@@ -235,7 +235,7 @@ config XSM_FLASK_AVC_STATS
 
 config XSM_FLASK_POLICY
        bool "Compile Xen with a built-in FLASK security policy"
-       default y if "$(XEN_HAS_CHECKPOLICY)" = "y"
+       default y if "$(HAS_CHECKPOLICY)"
        depends on XSM_FLASK
        ---help---
          This includes a default XSM policy in the hypervisor so that the
-- 
Anthony PERARD